Henry Gray (18251861). Anatomy of the Human Body. 1918.
passing into a dental canaliculus, the inner being continuous with the processes of the connective-tissue cells of the pulp matrix.
The solid portion of the tooth consists of (1) the ivory or dentin, which forms the bulk of the tooth; (2) the enamel, which covers the exposed part of the crown; and (3) a thin layer of bone, the cement or crusta petrosa, which is disposed on the surface of the root.
The dentin (substantia eburnea; ivory) (Fig. 1007) forms the principal mass of a tooth. It is a modification of osseous tissue, from which it differs, however, in structure. On microscopic examination it is seen to consist of a number of minute wavy and branching tubes, the dental canaliculi, imbedded in a dense homogeneous substance, the matrix.
FIG. 1005 Vertical section of a tooth in situ. X 15. c is placed in the pulp cavity, opposite the neck of the tooth; the part above it is the crown, that below is the root. 1. Enamel with radial and concentric markings. 2. Dentin with tubules and incremental lines. 3. Cement or crusta petrosa, with bone corpuscles. 4. Dental periosteum. 5. Mandible. (See enlarged image)
The dental canaliculi (dentinal tubules) (Fig. 1008) are placed parallel with one another, and open at their inner ends into the pulp cavity. In their course to the periphery they present two or three curves, and are twisted on themselves in a spiral direction. These canaliculi vary in direction: thus in a tooth of the mandible they are vertical in the upper portion of the crown, becoming oblique and then horizontal in the neck and upper part of the root, while toward the lower part of the root they are inclined downward. In their course they divide and subdivide dichotomously, and, especially in the root, give off minute branches, which join together in loops in the matrix, or end blindly. Near the periphery of the dentin, the finer ramifications of the canaliculi terminate imperceptibly by free ends. The dental canaliculi have definite walls, consisting of an elastic homogeneous membrane, the dentinal sheath of Neumann, which resists the action of acids; they contain slender cylindrical prolongations of the odontoblasts, first described by Tomes, and named Tomes fibers or dentinal fibers.